This invention relates to alpha-olefin polymerization catalysts, and more particularly to catalysts comprising the reaction product of an alkyl aluminum halide and the reaction product of a titanium (IV) amide compound and a magnesium (II) alkoxide or oxyhalide.
In the lower pressure polymerization of alpha-olefins substantial economic benefits can be derived by carrying out the polymerization in the presence of highly active catalysts such that polymeric products are produced in yields high enough to eliminate the need for removal of catalyst residues. To this end catalyst comprising an organoaluminum promoter and a Group IV metal amide compound have been proposed.
One such catalyst, described in Belgium Patent No. 661,389 to Farbwerke Hoechst A. G. consists of a trialkyl or triaryl aluminum compound, and a compound of the formula R.sub.4-n M(NR').sub.2 in which M is a Group IV metal, R is a hydrocarbon or hydrocarbonoxy group, R' is hydrogen or an alkyl or aryl group and n is 1-4. However, the catalyst has the drawback that residues need to be removed. For example, the titanium compound (isobutoxy).sub.2 Ti(NCH.sub.3).sub.2 in heavy oil was cooled to -5.degree. C. and then activated with an organo aluminum promoter at 65.degree. C. and employed in the polymerization of alpha-olefins. After polymerization, an organo alcohol is added to the mixture, the polymer is separated by filtration, washed with water and acetone and dried at 100.degree. C. A similar catalyst and process is described in Belgium Patent No. 664,699.
Another such catalyst, described in Japanese Patent 15,980 (1965), is a binary catalyst system consisting of organo-aluminum compounds and Ti(NR.sub.2).sub.n X.sub.4-n where R is an alkyl group, X is halogen and n is 1-4. After polymerization, the product is washed with HClmethyl alcohol.
Another such catalyst described by Koide, et al. in the Journal of Polymer Sciences (Polymer Chem) 11:3161 (1973) polymerizes styrene but the polymerization activity of the catalyst system, Ti(N Et.sub.2).sub.4 -AlMe.sub.3, is described as not very great. It was found that the polymer yield was dependent on the Al/Ti molar ratio with an optimum activity at an Al/Ti molar ratio of 1.5 or thereabouts. When the Al/Ti molar ratio was above 4, no polymerization occurred.
Accordingly, as can be appreciated from the foregoing, it would be desirable to improve the above catalysts of the type wherein a Group IVB metal and nitrogen compound is involved as a catalytic component while retaining the desirable polymerization and solubility properties thereof and avoiding the necessity of removing the catalyst residues.
It is an object of this invention to provide such an improved catalyst and a method for the preparation thereof. A further object of the invention is to provide for the polymerization of alpha-olefins in the presence of the invented catalysts. A further object of this invention is to provide a catalyst which is sufficiently active that polymeric product is produced in yields high enough to eliminate the need for removal of catalyst residues. Other objects of the invention will be apparent to persons of skill in the art from the following description and the appended claims.
It has now been found that the objects of this invention can be achieved by reacting a magensium (II) compound with a Group VIB or VB amide compound under conditions such that an easily handled reaction product is obtained, and then reacting this product with an alkylaluminum compound to form a solid catalyst component. Similar to the catalyst comoponents of Belgium Patents Nos. 661,389; 664,699; Japanese Patent No. 15,980, the invented components can be promoted with an organoaluminum promoter and employed in the polymerization of alpha-olefins to polymers having a relative broad molecular weight distribution. However, sufficiently high yields are obtained with the catalyst of the instant invention that separation of catalyst residues from the polymeric product is unnecessary.